Lesson Note on Mass-Volume Relationships: Meaning, Mole Concept and STP for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS 2)
Term: 1st Term
Week: 7
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemical Reactions
Previous Lesson: Chemical Reactions: Chemical Equilibrium and Le Chatelier’s Principle.
Topic: MASS VOLUME RELATIONSHIPS
Subject Matter: Meaning of mass-volume relationships (link between mass, moles and volume in reactions), mole, molar quantities, molality, standard temperature and pressure STP, relative densities, relative molar mass

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

• Define mole, molar quantities, molality, standard temperature and pressure (STP), relative densities, and relative molar mass.
• State the units for mole, molar mass, molality, and molar volume.
• Explain the link between mass, moles, and volume in chemical reactions.

Affective Domain:

• Appreciate the importance of mass-volume relationships in quantitative chemical analysis.
• Develop an interest in solving chemical calculation problems.

Psychomotor Domain:

• Calculate the mass of reactants and products given relevant information.
• Determine the number of moles of reacting substances and products in chemical reactions.
• Solve problems involving molality and molar volume at STP.

Social Domain:

• Work collaboratively to solve chemical calculation problems.
• Communicate their understanding of mass-volume relationships effectively.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio
• https://www.chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/03%3A_Stoichiometry%3A_Calculations_with_Chemical_Formulas_and_Equations/3.05%3A_Calculations_Involving_Molar_Mass_and_Number_of_Moles
• https://www.britannica.com/science/molality

Instructional Materials

The teacher will teach this lesson with the aid of:

• Students’ textbooks
• Students’ workbooks
• Periodic table
• HCl, NaOH, magnesium ribbons, copper, copper oxide (for demonstration of concepts if practicals are integrated)

Rationale for the Lesson

This lesson helps pupils understand how to quantify substances in chemical reactions. It provides fundamental knowledge needed for accurately predicting reactant and product amounts, which is essential for further studies in chemistry and various industrial applications.

Prerequisite/Previous Knowledge

Pupils are expected to have prior knowledge of basic concepts of atoms, molecules, chemical equations, balancing equations, and the mole concept from Junior Secondary School and Senior Secondary School 1.

Lesson Content/Board Summary

MASS-VOLUME RELATIONSHIPS

Introduction to Mass-Volume Relationships

Mass-volume relationships describe the quantitative link between the mass, moles, and volume of substances involved in chemical reactions. These relationships are essential for predicting the amounts of reactants and products.

The Mole Concept

The mole is the SI unit for the amount of substance. It is defined as the amount of substance that contains as many elementary entities (atoms, molecules, ions, electrons, etc.) as there are atoms in 0.012 kilogram of carbon-12.

Key definitions:

• Avogadro’s Number (N_A): The number of particles in one mole of any substance, approximately 6.02 x 10²³ particles/mol.
• Molar Mass (M): The mass of one mole of a substance, expressed in grams per mole (g/mol). It is numerically equal to the relative atomic mass or relative molecular mass.

Standard Temperature and Pressure (STP) and Molar Volume

Standard Temperature and Pressure (STP): Defined as a temperature of 0°C (273 K) and a pressure of 1 atmosphere (101,325 Pa or 760 mmHg).

Molar Volume: At STP, one mole of any ideal gas occupies a volume of 22.4 dm³ (or 22,400 cm³). This is known as the molar volume of a gas at STP.

Molality

Molality (m) is a measure of the concentration of a solute in a solution in terms of amount of solute in a given amount of solvent. It is defined as the number of moles of solute per kilogram of solvent.

Formula:

Molality (m) = (Moles of solute) / (Mass of solvent in kg)

Unit: moles per kilogram (mol/kg).

Relative Densities

Relative density (or specific gravity) is the ratio of the density of a substance to the density of a reference substance, usually water for liquids/solids, or air/hydrogen for gases. It has no units.

Relative Molar Mass

Relative molar mass is the ratio of the molar mass of a substance to 1/12th of the molar mass of a carbon-12 atom. For practical purposes, it is the sum of the relative atomic masses of all atoms in a molecule.

Calculations Involving Mass-Volume Relationships

Key formulas:

• Number of moles (n) = Mass (g) / Molar Mass (g/mol)
• Number of moles (n) = Volume (dm³) at STP / 22.4 dm³/mol (for gases)
• Number of moles (n) = Number of particles / Avogadro’s Number (N_A)

Example 1: Calculate the number of moles in 44g of CO₂. (C=12, O=16)

Step 1: Determine the molar mass of CO₂.

Molar mass of CO₂ = 12 + (2 × 16) = 12 + 32 = 44 g/mol

Step 2: Use the formula for number of moles.

Number of moles = Mass / Molar Mass

Number of moles = 44 g / 44 g/mol = 1 mol

Therefore, there is 1 mole in 44g of CO₂.

Example 2: What volume will 0.5 moles of oxygen gas occupy at STP?

Step 1: Recall the molar volume of a gas at STP.

1 mole of any gas occupies 22.4 dm³ at STP.

Step 2: Calculate the volume for 0.5 moles.

Volume = Number of moles × Molar Volume at STP

Volume = 0.5 mol × 22.4 dm³/mol = 11.2 dm³

Therefore, 0.5 moles of oxygen gas will occupy 11.2 dm³ at STP.

Example 3: Calculate the molality of a solution containing 36 g of glucose (C₆H₁₂O₆) in 250 g of water. (C=12, H=1, O=16)

Step 1: Determine the molar mass of glucose.

Molar mass of C₆H₁₂O₆ = (6 × 12) + (12 × 1) + (6 × 16) = 72 + 12 + 96 = 180 g/mol

Step 2: Calculate the number of moles of glucose.

Moles of glucose = Mass / Molar Mass = 36 g / 180 g/mol = 0.2 mol

Step 3: Convert the mass of solvent to kilograms.

Mass of water = 250 g = 0.250 kg

Step 4: Calculate the molality.

Molality = Moles of solute / Mass of solvent in kg

Molality = 0.2 mol / 0.250 kg = 0.8 mol/kg

Therefore, the molality of the solution is 0.8 mol/kg.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils, checks their previous knowledge about the mole concept and balancing chemical equations by asking a few questions.
Pupils’ Activity: Pupils respond to the teacher’s greetings and answer the questions based on their prior knowledge.
Learning Point: Pupils recall previous knowledge relevant to the new topic.

Step 2: Explanation of Mole, Molar Mass, and Avogadro’s Number

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines the mole, explains Avogadro’s number, and describes how to calculate molar mass from atomic masses.
Pupils’ Activity: Pupils listen attentively, take notes, and ask questions for clarification.
Learning Point: Pupils understand the fundamental definitions of mole, Avogadro’s number, and molar mass.

Step 3: Explanation of Molar Volume and STP

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines Standard Temperature and Pressure (STP) and explains the concept of molar volume for gases at STP, providing the value (22.4 dm³).
Pupils’ Activity: Pupils listen, copy notes, and comprehend the conditions of STP and the significance of molar volume.
Learning Point: Pupils learn about STP and how it relates to the volume of gases.

Step 4: Explanation of Molality, Relative Densities, and Relative Molar Mass

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines molality, relative densities, and relative molar mass, explaining their formulas and units where applicable.
Pupils’ Activity: Pupils listen, take notes, and ask questions to clarify their understanding of these concepts.
Learning Point: Pupils learn about different ways to express concentration and relative quantities.

Step 5: Worked Examples on Mass-Mole-Volume Calculations

Time: 8 minutes
Teaching Skill: Demonstration/Problem-solving
Teacher’s Activity: The teacher solves example 1 and example 2 from the board summary on the board, showing step-by-step calculations for mass-to-mole and mole-to-volume conversions.
Pupils’ Activity: Pupils observe the teacher’s steps, ask questions, and copy the worked examples into their notebooks.
Learning Point: Pupils learn the practical application of the formulas in solving problems.

Step 6: More Worked Examples/Practice

Time: 6 minutes
Teaching Skill: Guided Practice
Teacher’s Activity: The teacher guides pupils through example 3 (molality calculation) and provides a similar practice question for pupils to attempt in class.
Pupils’ Activity: Pupils actively participate in solving the examples, attempt the practice question, and compare their answers.
Learning Point: Pupils gain confidence and reinforce their understanding through practice.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Define the term “mole”.
2. State the value of molar volume for any gas at STP.
3. What is molality, and what are its units?
4. Calculate the number of moles in 88g of CO₂. (C=12, O=16)

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 1 minute
Teaching Skill: Summarization
Teacher’s Activity: The teacher briefly summarizes the key concepts of mass-volume relationships and assigns homework, which includes practice problems from the textbook.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their learning and prepare for further practice.

Lesson Keywords

• Mole – The SI unit for amount of substance.
• Molar Mass – The mass of one mole of a substance.
• Molar Volume – The volume occupied by one mole of a gas at STP.
• STP – Standard Temperature and Pressure (0°C and 1 atm).
• Molality – Moles of solute per kilogram of solvent.
• Relative Density – Ratio of a substance’s density to a reference density.
• Relative Molar Mass – Sum of relative atomic masses in a molecule.

Differentiation

For struggling learners, the teacher will provide simplified examples and step-by-step guidance, focusing on one concept at a time. Advanced learners will be given more complex problems involving multiple conversions or real-world application scenarios, encouraging them to explore additional resources.

Note for teachers using this lesson plan

Teachers should ensure a periodic table is available for all pupils. Emphasize the importance of units in all calculations. Encourage pupils to show all steps in their problem-solving to identify areas needing improvement. Practical demonstrations or virtual simulations can enhance understanding of gas volumes and molar concepts.